With certain types of vehicles, it is desirable to have a dual or variable rate leaf spring construction. For example with light trucks, it is desirable to have a soft ride under normal driving conditions, but the spring should also have the capability of carrying heavy loads. To obtain a variable spring rate, multiple steel leaves have been used which incorporate leaves of decreasing lengths. The main leaf will carry the load under normal driving conditions, but when a heavy load is encountered, the main leaf will deflect downwardly into contact with the secondary leaves to increase the spring rate to the designed level.
Recently there has been substantial activity in the development of fiber reinforced resin leaf springs due to the fact that they have a substantially lesser weight than conventional steel leaf springs. However, it is extremely important to eliminate stress concentations in the fiber reinforced resin spring. Any sharp point of contact can cause a stress concentration which can result in premature failure. In view of this, there has been a need for a dual rate, fiber reinforced resin spring which will prevent any undue stress concentration in the main spring under heavy load conditions.